This invention relates to radiation cured conjugated diene block copolymer compositions which are cured at low radiation doses. Further, the invention relates to unsaturated crosslinked epoxidized polymer adhesive, coating, and sealant compositions.
Curing of adhesives based on conjugated diolefins and, optionally, vinyl aromatics has increased the range of service properties for such adhesives. Radiation curing of polymers to make such adhesives is known. Curing of coatings and sealants based on these polymers has reduced solvent content required for such products. This curing causes covalent crosslinking of the polymerized conjugated diolefins which is evidenced by a high gel content of the crosslinked polymer. Before crosslinking, the polymers are melt and solution processable but after crosslinking, the gel cannot be processed as melts or in solution. Crosslinking therefore enhances solvent resistance and improves elevated temperature shear properties, toughness and cohesion. Compositions can therefore be applied to a substrate in a melt or from solution and then crosslinked to form a superior adhesive, coating or sealant. However, improvements in the adhesives, coatings and sealants could be made if the adhesives could be cured at lower dosages of radiation.
Further, the known curable adhesives, sealants and coatings which are based on vinyl aromatics and conjugated diolefins do not have particularly good long term heat, weather and ultraviolet stability due to the need to utilize unhydrogenated polymers. The known vinyl aromatic-conjugated diolefin based adhesives, coatings and sealants which are curable are unhydrogenated polymers. Hydrogenation is known to improve long term heat, weather and ultraviolet stability, but it removes the double bonds which are needed to effect the curing by radiation crosslinking. Such curing methods are not effective when the polymers are hydrogenated. The requirement for this unsaturation is particularly evident when typical tackifiers are present in the compositions because their presence generally inhibits crosslinking of the polymer.
It is an object of the present invention to provide a block copolymer composition which can be crosslinked by low doses of radiation, and which is easily processable in the melt or at high solids content before crosslinking but has a high gel content after crosslinking. Further, it is an object of this invention to provide an adhesive, coating or sealant composition which is based on this crosslinked block copolymer.